It is common practice to admit patients to an intensive care unit (ICU) after major surgery for close post-operative monitoring. However it is unclear whether using the ICU for post-operative monitoring actually improves outcomes. In fact, admission to an ICU following major surgery represents an intervention associated with possible benefits (early detection and management of potentially life 5 threatening complications) but also with risks and drawbacks (e.g. exposure to multi-drug resistant organisms, iatrogenic injuries from invasive monitoring, sleep deprivation and increased risk of delirium). Additionally, admissions to the ICU have a significant impact on healthcare expenses. ICU admissions represent about 13% of hospital costs, 4.2% of national health expenditures, and 0.56% of gross domestic product. 10 Currently, there are no standard criteria for admission to the ICU after major surgical procedures, and about one third of patients undergoing major surgery are either over-triaged to the ICU or under- triaged to a regular ward. Over-triage to the ICU may result in unwanted adverse events and harm to patients, as well as significantly adding to the cost of health care. Under-triage to a lower level of care might lead to worse outcomes through failing to recognize or adequately manage treatable problems. 15 Our overarching research aim is to develop objective criteria for ICU admission after major surgical procedures to enhance post-operative triage to the appropriate level of care. The goal of this pilot proposal is the initial identification of peri-operative conditions, measurable parameters, that could be used to improve post-operative triage. Additionally, we will also investigate whether objective criteria or subjective clinical judgment (the current standard of care) have the 20 closest correlation with events mandating ICU admission. We will retrospectively identify patients that do require a post-operative ICU admission as those for which certain key events have been recorded during the immediate post-operative course (e.g. prolonged endo-tracheal intubation or re-intubation, hemodynamic instability requiring vasopressors, respiratory or circulatory arrest). We will then use three complementary strategies to identify criteria for 25 post-operative triage to the ICU. ? A retrospective analysis will identify what peri-operative conditions or risk scores correlate with key events requiring ICU management. ? A prospective pilot study of 100 patients will clarify whether subjective clinical assessments or objective parameters and risk scores have the closest correlation with key events requiring ICU 30 management. ? An expert panel will establish consensus criteria for postoperative ICU admission based on their own expertise, as well as on the data collected during our study. A subsequent Investigator-Initiated Research proposal will assess how those criteria can be implemented in standardized guidelines or decision-making tools to enhance post-operative triage, 35 improve patient safety, and decrease costs of healthcare delivery. Our ultimate goal is to evaluate current triage methods and implement standardized decision making processes to improve patient safety and decrease costs related to inappropriate utilization of the ICU.